Corn rootworms are the most serious pests of corn in the major corn growing regions of North America. Root feeding of the larvae has a pronounced effect on corn growth and corn yields. Corn rootworm infestations have been shown to decrease yields of corn by 13 to 16 bushels per acre. The present day toll paid by U.S. farmers in treatment costs and crop losses is estimated to be in the range of $1 billion per year.
Since crop rotation is the only practical, non-chemical control for corn rootworms [e.g., Western Corn Rootworm, Diabrotica virgifera virgifera (LeConte), and Northern Corn Rootworm, D. barberi (Smith and Lawrence)], there has been heavy reliance placed on the use of chemical insecticides. However the present day control of corn rootworms with soil insecticides has been complicated by additional technological problems. Not only has low levels of resistance developed to some of the newer insecticides, but accelerated microbial degradation has been noted where the soil microorganisms have developed a capacity to use the soil insecticide. Such has resulted in degradative rates of carbofuran and other soil pesticides as much as 10-fold higher in problem soils than in non-problem soils. These adverse factors, together with legal restrictions on use of insecticides because of potential user toxicity and environmental contamination, resulted between 1950 and 1983, in the withdrawal of recommendations for use of the following soil insecticides for corn rootworm control: benzene hexachloride, aldrin, dieldrin, heptachlor, chlordane, parathion, diazinon, disulfoton, fensulfothion, isofenphos, carbaryl, metalkamate, landrin, and carbofuran. Only a few new insecticides have been introduced during the 1980's as replacements. Thus the prognosis for long-term continuation of successful soil insecticide control of rootworms does not look promising.
There are a number of parasporal-body-forming Bacilli that produce toxins for insect larvae. A number of soil bacteria effective in the control of insects of several orders have been commercially available since the 1960's. Examples are Bacillus popilliae for the control of Japanese beetle (Scarabaridae), several serotypes of Bacillus thuringiensis for the control of Lepidoptera pests of food and fiber crops and B. thuringiensis subsp. israelensis effective on Diptera, i.e., mosquitoes and black flies. A more recent isolate, B. thuringiensis subsp. tenebrionis, seems to be toxic to certain Coleoptera, that is, the Colorado potato beetle. In all cases, perhaps with the exception of B. popilliae, the bacteria produce a proteinaceous parasporal inclusion during sporulation. Generally, it is this inclusion which contains the lethal agent; that is, it is composed of protoxin molecules which are cleaved in the larval gut to toxins. In a few cases, the bacterial spore may also participate in the killing, and in the case of B. popilliae (and a few less prevalent related organisms), it is probably the multiplication of the bacterium in the larval haemolymph that results in the death of the host.
There has been no isolation/description of soil bacteria that are effective on the coleopteran species, Diabrotica (corn rootworm).
In view of the above-mentioned technological limitations on chemical control of corn rootworm, including Pest resistance, non-biodegradability, and animal toxicity, a biological control agent for corn rootworm would be a most desirable alternative. Accordingly, this invention is directed to the use of parasporal-inclusion-forming Bacillus laterosporus, which when present in the soil of growing corn crops are effective for controlling corn rootworm infestations. Compositions comprising (1) viable parasporal-inclusion-producing bacteria of the species Bacillus laterosporus in the form of vegetative cells or spores, and (2) an agriculturally acceptable carrier therefor can be applied to the soil in conjunction with (either before, with or after) planting of a corn crop.